JPS6017009B2 - Method and device for removing contaminants from aluminum - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to the removal of alkali metal and alkali metal contaminants from molten aluminum by reaction with aluminum fluoride.

The molten aluminum removed from the electrolytic reduction tank contains small amounts of alkali metals such as lithium and sodium, and alkali metals such as magnesium and calcium.

The presence of these contaminants, alkali metals and alkali metals, is detrimental to the various applications to which such primary aluminum metals are intended. For example, in the manufacture of sheets or plates of magnesium-containing aluminum alloys, sodium in amounts of about two feet or more can cause "hot shortness" or green cracking during hot rolling.

The presence of trace amounts of lithium and/or sodium
Increases the rate of oxidation of molten aluminum. This increases melt losses and creates a thick layer of dross that can block the caster nozzle and reduce metal flow. Therefore, from an economic and technical point of view, it is desirable to remove these contaminant elements as soon as possible after removal of the primary aluminum from the electrolytic reduction tank so that the molten aluminum containing lithium and/or sodium is exposed to the atmosphere. It is necessary to shorten the time. Small amounts of magnesium are detrimental to electrical conductivity and should therefore be removed from primary aluminum to be used for products where its electrical properties are important. Accordingly, it has been identified as desirable to reduce the concentration of alkali metal and alkali metal contaminants to a diagonal or preferably below. Such removal may be due to the fact that aluminum or aluminum-based alloys (the term "aluminum" is used herein to broadly include pure aluminum as well as its alloys) contain small amounts of alkali metals and/or alkali metals. It is also desirable in other cases of metal contamination. The content of alkali metals and/or alkali metals in the dissolved state is such that the content of alkali metals and/or alkali metals in the dissolved state is
It is also known that scales can be reduced by contacting with aluminum fluoride-containing substances. These contaminants react with the aluminum fluoride to form some compounds that are desirable to mix (eg, cryolite-based compounds such as MaruF, FunaF, 2A〆F8). Aluminum fluoride, typically in the form of solid particles, is contacted with molten aluminum. The aluminum fluoride treatment agent may consist primarily of aluminum fluoride or may consist solely or partially of an alkali metal fluoroaluminate that is solid at the temperature of the molten metal. Examples of the latter type of treatment agents (those useful for the removal of lithium, magnesium, and calcium) are granular sodium chloride, or lithium-free electrolyte with a low weight ratio of sodium fluoride to aluminum oxide. It is a bath electrolyte and therefore contains aluminum fluoride in excess of the stoichiometric amount of Nabuso F3, and has a composition such that it remains solid at the processing temperature. This is usually the case when said ratio is in the range 1.3 to 1.5. In fact, it is not a requirement that the additives remain solid; low melting point (approximately 725°C) compounds containing a large excess of ASOF3, which melt when introduced into molten aluminum, are also suitable for alkali may be equally effective in removing metals or alkali metals (such compounds may be
aF:A〆F3 weight ratio). Such active compounds may also contain inert substances such as aluminum oxide in proportions as high as 5% by weight, although 7-30% is the usual aluminum oxide content of commercial aluminum fluoride. . Treatment with aluminum fluoride is believed to be advantageous for the removal of alkali metals and alkali metals compared to fluxing with chlorine gas or chlorine/inert gas mixtures because: This is because operations using such gases produce harmful by-product gases and are otherwise inconvenient.

U.S. Patent No. 3,305,351 and U.S. Patent No. 3 using AsoF3
In known processes such as those described in Nos. 52, 01 and 4,138,246, molten aluminum is mixed with solid particulate materials containing aluminum fluoride, either alone or mixed with carbonaceous materials (e.g. coke), in the form of a filling stock. Pass through the furnace bed.
U.S. Pat. No. 4,277,280 discloses coarse jaw grains A-F
A similar effect is achieved by passing molten aluminum upward through a reactive bed (not a filter) of 3-containing material. However, the use of bed filters or reactive beds composed of reactive materials has several drawbacks. Most of the products of the reaction of alkali metals (Li, Na, Mg) with aluminum fluoride remain trapped on or within the reactive bed or combined filter material and quickly become clogged. . Electrolyte from the electrolytic reduction cell, sludge and/or other solid and liquid impurities carried with the molten metal from the electrolytic cell have similar adverse effects. For similar reasons, selective metal pathways or "channels" may appear within the reactive bed, significantly reducing alkali metal removal efficiency. The aluminum fluoride agent is depleted during the processing of molten aluminum, so the capacity of the reactive bed is not constant during its service life.
To prevent thermal hydrolysis of the aluminum fluoride and metal loss in the reactive bed, the aluminum fluoride is preferably completely submerged in the molten aluminum at all times.

However, this requires constant heating and heat consumption even when the equipment is not in operation, which increases the cost of the process. Changes in the composition of metals processed in such systems are always accompanied by metal losses. Furthermore, decomposition due to thermal hydrolysis (ie, reaction with water in the combustion products) is likely to occur during the initial heating of the A〆F3 bed. Effective contact between loosely packed aluminum fluoride particles and molten aluminum metal is difficult to achieve.

This is because the aluminum fluoride powder floats on the surface of the molten aluminum due to the high surface tension of the molten aluminum and the large density difference between the aluminum fluoride powder and the molten aluminum. Additionally, aluminum fluoride powder does not leak easily with molten aluminum and is very thermally stable (ie, does not melt under atmospheric pressure). Also, aluminum fluoride is about 1270
The reaction between liquid-liquid or gas-liquid phase occurs at the processing temperature of molten aluminum (approximately 660 to 900
qC) is not possible. These physical properties demonstrate the unsatisfactory success of prior art attempts to introduce loose particulate aluminum fluoride into molten aluminum. It is possible to inject aluminum fluoride particles into molten aluminum with a jet of carrier gas, such as air or nitrogen, using an injection launcher. However, injection operations require considerable time, can be hazardous due to high gas pressures in the molten metal, and furthermore, the use of air as a carrier gas can lead to excessive dross and oxide film formation. sell. It is also possible to add a large amount of aluminum fluoride powder to the bottom of the empty rubbo before introducing the molten metal. However, the aluminum fluoride powder reacts selectively with the electrolyte from the electrolytic cell (which is necessarily siphon-transferred from the electrolytic cell along with the molten aluminum) to form a solid mass that remains attached to the crucible lining. It recognized. Therefore, effective contact with molten aluminum is prevented.As is clear from the above considerations, efficient contact between the loosely packed particles of ASOF3-containing material and the alkali metals and alkali metals in the molten aluminum metal. The reaction requires considerable contact time. In the method of the present invention, a treatment agent is applied to molten metal under conditions that suppress excessive turbulence (ripples) on the surface of the molten metal in order to recirculate the treatment agent within the molten metal and at the same time reduce oxidation of the metal. It is necessary to add an appropriate amount of (AsoF3 or AsoF3-containing substance).

In the method of the present invention, the processing agent is entrained and transferred into the molten metal by supplying the processing agent into the vortex generated in the molten metal body held in a container (rubbo). The swirl generator also functions to generate an upward swirling flow in the molten metal in the boundary region of the vessel to maintain prolonged contact between the treatment agent particles and the molten metal. Circulation of the molten metal by creating a vortex continues for a sufficient period of time to reduce the alkali metal and alkaline metal content in the molten metal to a desired low value, at which point the circulation is stopped. Some of the reaction products mixed with residual treatment agents rise to the metal surface in the form of dross, and from such dross the molten metal is removed by skimming the dross or by siphoning the metal, or by other conventional methods. It can be separated by However, a large portion of the reaction products tend to stick to the lining of the crucible during the processing process, so some waste disposal methods allow the molten metal to be removed when the crucible is empty. It is well known to introduce reactive substances into a molten metal vortex generated in a vessel which discharges as a continuous stream.

In the operation of the process of the invention, the generation of vortices is used as a means to bring into contact finely divided particulate material of relatively low bulk density with molten metal and to disperse particles of material in such molten metal. It also serves both functions as a means to maintain close contact with the molten metal for an extended period of time until the vortex is terminated. The vortex is preferably generated and maintained using a rotary sludge speculator having a multi-bladed rotor with beveled blades immersed in the molten metal in the rubbo and rotated about a vertical axis, the sludge of each blade being Preferably, the angle is such that the blade has a major downward facing surface at an acute angle to the vertical.

Preferably, the impeller rotor is arranged eccentrically in the Lubbo with respect to the vertical centerline of the Lubbo. It is also possible to generate swirls using electromagnetic induction flies. A suitably arranged induction coil is placed outside the rubbo or other vessel containing the molten metal. The present invention also provides an apparatus for mixing particulate A〆F3 treatment agent with molten aluminum.

The lozenge includes a lupus and an impeller or rotor for containing molten metal, the impeller having oblique blades and being eccentrically located from the vertical centerline of the lupus. Specific ranges of their dimensions and positional relationships will be explained below. In the accompanying drawings, a cylindrical rubbo 10 contains molten aluminum 11.

The separation lid 12 supports an eccentric impeller 14, which is driven by a motor 16. The impeller 14 has blades 20 immersed in the molten aluminum 11.
It has a rotating shaft 18 with a The lid 12 also includes a duct 22 for supplying processing agents to the crucible and an exhaust conduit 24 for exhausting fumes from the crucible. Typically, a crucible is a steel shell with a refractory lining that is inert to molten aluminum. The lid 12 and associated components are used to store batches of molten metal contained in a series of different mobile crucibles. The Lubbo 10 is a movable vortex generator assembly so that the same fly coating layer can be used to remove the alkali metals from the molten aluminum. A suitable amount of molten aluminum metal is charged into the tank.

Lid 12 is then placed on top of Rubbo and the vaned portion of impeller 14 is immersed in molten aluminum. A granular treatment agent consisting of or containing aluminum fluoride (ASOF3), which is solid at the temperature of molten aluminum, is fed by gravity via duct 22. Rotation of the impeller is preferably started before (but may be started after) the introduction of the treatment agent and maintains a stable vortex (26 in FIG. 2) in the melt 11. Directional flow of components into the molten metal by the generation of swirls
and radial flow component
This results in a combination of The AsoF3 particles are drawn into the vortex and then circulated through the melt generally along the flow path shown at 28. Direct coupling of aluminum fluoride into the vortex is not necessary because the aluminum fluoride agent is rapidly moved into the vortex by the high circulation rate of the metal at the melt surface. The rotation of the impeller creates a gap between the alkali metal and/or alkali metal (i.e., dissolved contaminants) and evolved aluminum sufficient to reduce the contaminant content in the melt to a desired low level. The vortex 26 and recirculation of the aluminum fluoride particles are continued until the reaction has taken place.

Typically, the time required to achieve such results is less than about 1 minute, and in fact much less than 10 minutes. Compounds such as cryolite-based compounds produced by the reaction of contaminants alkali metals and alkali metals with aluminum fluoride float on the surface of the melt, thus stopping the rotation of the impeller; When the lid is removed from the Rubbo, it can be easily removed by skimming or other methods. The decontaminated metal can then be poured or otherwise removed from the rubbo. The method of the present invention reduces contaminant concentrations from typical concentrations of IJ thium of about 2 pm and sodium of about 30 to 6 pm in a continuous cycle of 1 minute or less at the impeller. By doing so, it can be reduced to less than 1 skin.

A satisfactory reduction in the content of contaminant metals (e.g. 2 ppm Li It is now possible to achieve even greater reductions in energy consumption in a shorter time. Although aluminum fluoride may contain a proportion of alumina, the fluxing action of the fluoroaluminate reaction product is effective in removing such insoluble alumina. In fact, it has been observed that the process of the present invention exhibits the additional effect of removing inclusions such as aluminum carbide (A4C3) which were present in the melt before treatment. The optimum combination of directional and radial (radial) flow components to achieve high incorporation efficiency of solid ASOF3 particles into molten aluminum can be achieved by properly positioning the impeller with respect to Rubbo and/or Alternatively, this can be achieved by the dimensions and configuration of the impeller.

For this purpose, the impeller is equipped with a plurality of equiangularly arranged and pitched blades, each blade having a main surface 2 facing downward at an acute angle to the vertical.
0a. The center of the rotation axis of the impeller is located eccentrically from the Lubbo geometric axis,
Further, in the rotating direction of the impeller, the surface 20a of the blade serves as a lead surface (advance surface) of the blade, and a force having a downward component is applied to the molten aluminum. In the drawing, ■ (theta) indicates the oblique angle (pitch angle) of the blade surface 20a, d indicates the overall diameter of the blade portion of the impeller, h represents the height dimension of the blade, and x represents the height of the impeller. y indicates the eccentric distance of the rotation axis, y indicates the vertical distance from the inner bottom of the Rubbo to the midpoint of the impeller blade, and y indicates the vertical distance from the inner bottom of the Rubbo to the stationary surface of the molten metal in the Rubbo. , D indicates the inner diameter of the lupus, and arrow R indicates the rotation direction of the impeller. According to the invention, as a particular or preferred embodiment thereof, the following ranges of relative relationships and dimensions are found in the form and arrangement of an impeller of the type shown in the accompanying figures.

Satisfactory results can be obtained with impellers placed in the center of the cylindrical vessel (Rubbo) or with impellers that are hardly eccentric, but the eccentricity (x) of the impeller's axis of rotation is usually between 0.1 and
The range is 0.2 arc, more preferably 0.25 to 0.
The range is 7d.

Three blades with a pitch angle of 30 to 350, spaced 1200° apart, and a d/D ratio of about 0 were used.

Most preferably, it is 25.

The eccentricity x of the impeller is most preferably 0.9. The described impeller arrangement is advantageous in creating a stable vortex without the use of vertical baffles, which are impractical in replaceable transfer rubbos. The function of conventional baffles in generating vortices by maintaining a high relative velocity between the impeller and the liquid is due to the combination of both radial and axial flow components created by the impeller. This is achieved with the inventive impeller arrangement. 450 feathers
A pitch angle (pitch angle) as large as
For example, it is preferable to push the molten metal aluminum downward using a 3-3-3 screw to draw the aluminum fluoride powder into the molten aluminum.

The required axial component of the molten metal flow is achieved by positioning the impeller eccentrically with respect to the geometric axis of the rubbo, even using an impeller with vertical blades.

However, in order to minimize waves and vibrations at the surface of the molten metal, it is highly preferred to use eccentrically spaced Pilch angled impellers. Due to the eccentricity of the impeller, splashes (
It has been found that it is possible to fill a larger amount of Rubbo without the risk of occurrence of splatting (splashing). Such an eccentric calendar is an important feature of preferred embodiments according to the present invention, since the impeller eccentric layer allows processing of substantially larger batches of metal with a rubbo of a given size. The minimum rotational speed for a given impeller is such that it will generate and maintain a stable vortex, while the maximum rotational speed is the one above which air will be entrained into the molten metal that is being crushed. This is the limit speed.

These values depend on the diameter d of the impeller. The optimum rotational speed is one that produces good swirl without excessive metal splashing or loss and without causing erosion of the Lubbo refractory material or impeller structure metal. Taking as an example an impeller that preferably provides a d/D ratio in the range 0.15 to 0.40, such impellers currently rotate at rotational speeds of about 100 to about 30 pm. It is preferable to let However, rotational speeds outside this range may be used as long as the desired swirl is thereby achieved without excessive splashing. The use of eccentric layer impellers with tilt or pitch vanes and rotating in the directions defined above provides a highly efficient combination of directional and radial flow components that enhances the penetration of the collective aluminum fluoride particles into the molten metal. It was found to be particularly satisfactory in terms of the generation of stable vortices. AsoF
During processing of molten aluminum at the 3 minute end, alkali metals and alkali metals react with F3 at A to form mixed alkali cryolite-based compounds.

For example, N is also 2F,2 in AZ3F,4, Na2LiA, F6, and Li3Na3A. These compounds have relatively low melting points and are easily agglomerated or adhered to the rubbo walls or floated on the melt surface, where they are removed whenever they are deposited with a siphon from the electrolytic cell. Reacts with cell electrolyte or metal oxides present. During the subsequent siphon metal transfer, most of these compounds remain inside the lupo and are thus separated from the purified molten aluminum. Although high-grade A-F3 is desirable for rapid reaction with alkali metals, low-grade A-F3 powder can be compensated for by addition to increase the A-F3/A-F3 ratio.

Other mixtures that may be used include low-grade A-F3 (e.g. A-F3 mixed with A-203) or very excessive A-F3.
Aluminum electroreduction bath material containing 〆F3 (ie, Na3A〆F6 containing excess A and F3). The invention is further illustrated by the following examples. Example 1 about 20
~2 A 130 kg sample of molten aluminum with a purity of 99.7% containing Li from mother blood was subjected to each of the following various operations.
Treated with solid AsoF3 ground to a particle size of minus (1) 35 mesh.

A: 3009 AsoF3 particles were supplied to the molten aluminum surface without sanding.

B: 200 μm of AZF3 particles were fed to the melt surface while the melt was being moved by a rotor rotating at 90 pm but without creating a swirl.

C: 300 ml of A-F3 particles were injected into the melt below the melt surface through a graphite launcher with nitrogen as a carrier gas. D: Inject 200 μm of Ag F3 particles as in C above, but the melt is stirred by a rotor (located above the launcher outlet) rotating at 90 μm.

E: A of 200 evenings (B-1) and 300 evenings (E-2)
According to the present invention, the F3 particles are supplied to the surface of the melt while generating and maintaining a vortex in the melt using a flywheel rotating at 20 pm.

In another operation F, A〆F3 was not used, but 90 p
The rotor rotated at m to stir the mixture without creating a vortex.

The results were as follows. Operation according to the method of the present invention (E
-1 and E-2) achieved tium removal significantly faster than any other procedure.

The concentration reached after 9 minutes by the procedure of the present invention was only comparable to that by procedure D, which used a combination of injection of AsoF3 and fly Azusa, which had a much lower initial concentration of lithium contamination.

The dimensions and arrangement of the impeller in this example are as follows.

The diameter d of the impeller is 12. & pine, and its impeller has four blades of 8.8 skin height, and those blades are 35 o.
The angle bothered me.

The diameter of the Lupo (container) is 5 to 1, and the daily value is 37.
5, the value of x was 1/2d.

Example 2 A series of amounts of molten aluminum contaminated with lithium and sodium were prepared using an apparatus of the type shown in the accompanying drawings with a cylindrical rubbo having an internal diameter of about 160 mm and a nominal volume of about 4500 molten aluminum. were treated by the method of the present invention.

In each case, fill the rubbobo to a height of 100 skins with molten aluminum and add A〆F3 to about 1 tonne of aluminum.
．． It was applied to the molten aluminum surface at a ratio of 7k9.
An impeller with slanted blades having a blade height of 25 arcs and a diameter of 45 degrees is offset from the center by 20 to 3 runs (preferably 22.
7.5 As an addition, the vane was immersed in molten aluminum so that the upper edge of the vane was located midway between the top surface of the molten aluminum and the bottom of the rubbo (so the vane was completely submerged within the bottom half of the molten metal body). ). In each case, the impeller was rotated for IQ minutes at a speed between about 130 and about 138 pm to generate and maintain a stable swirl. The addition method of A〆F3 particles and the molten metal temperature were changed for each test. The results of 20 consecutive tests were as follows.

(Notes on the table above) * Not measured * * a- Add 50* of Am F3 at the start, and add the remaining 50* after 1 minute of impeller operation.

b - 33 times at the start, 33 times after 30 seconds of impeller operation,
Add 33% after 1 minute. c-1.5 from the start of impeller operation
Continuously supplied per minute. d - 1.0 from the start of impeller operation
Continuously supplied per minute. e-0.5 from the start of impeller operation
Continuously supplied per minute. f - 33% added at the start, 33% added 15 seconds after the impeller started operating, and 33% added 30 seconds later. g-
33% added at start, 33*, 2 10 seconds after impeller starts
Added 33% after 0 seconds. These data demonstrate the adverse effect of high temperature on lithium removal efficiency, which is a thermodynamically dominated reaction between lithium fluoride and metallic lithium that prevents 100% IJ lithium removal efficiency from high temperature metals. This is due to the balance of lithium between the two. A similar effect was not observed with sodium due to its high vapor pressure which facilitates removal. The average removal efficiency of silicum after per-flour treatment was 93% for the 20 tests in the table above.

This is a satisfactory lithium concentration (
that is, below the upper limit that is acceptable for most purposes). Example 3 Several processing experiments were conducted in a transfer crucible containing aluminum transferred from an electrolytic reduction tank.

Aluminum fluoride powder used (92% A and F3, approx. 8
It had a high density of 1.5 to 1.7 particles/ground (%A203; weight), and had the following particle size distribution. 25%
>100 micron 50% >8
0 microns 75% >65 microns In these treatments, each rubbo contained approximately 3500 k9 of molten aluminum.

A three-blade impeller was used, which had a blade pitch (angle @) of 35o, a diameter (d) of 46 arcs, and a blade height (h) of 25 arcs, and rotated to form a stable spiral. generated and maintained.

The d/○ ratio and the h/day ratio were each 0.25, and the maximum treatment time was 6 minutes. The eccentricity (x) of the rotor is 1
/2d. Several rubbos were processed in series. For comparison purposes, one set (Test 1) was conducted without the use of aluminum fluoride. The remaining six treatments (tests 2-7) were according to the invention. In tests 2-5, all of the aluminum fluoride was added at or before the start of the rope, and in tests 6 and 7, only 1' of the aluminum fluoride was added.
3 at the start, 1'3 0.5 minutes after the start, and 1'3
was added 1 minute after the start. The metal in Rubbo in Test 7 initially contained 101 legs of magnesium. The other six tested metals contained less than the IQ cape of magnesium. The results were as follows.

Test 1 (comparison) shows alkali metal removal solely due to the aluminum rope effect.

Iridium removal efficiency after 3 and 6 minutes (15%, 19
%), the removal rate of sodium is higher in (61%).
%, 72%), due to the much lower vapor pressure of lithium than sodium.

In fact, sodium has a boiling point of 88 mm at atmospheric pressure, compared to lithium's boiling point of 132 mm. Tests 2, 3 and 4 compare the effects of the AsoF triple on sodium and lithium removal. A〆F
There was a significant effect on lithium removal by increasing the ratio of k9/A of 3 from 0.7 to 3.3.
This effect is less pronounced for sodium because oxidation alone results in rapid sodium removal. In test 5, the rotation speed was changed from 10pm to 15pm.
Same as Test 3 except that the enemy pm was increased.

With increasing rotational speed, the removal efficiency of sodium and lithium increased from 89% to 92% and 74%, respectively.
% to 85%. Test 6, using seven transfer rubbos, shows the effect of sequential addition of A〆F3 powder on alkali metal removal rate.

It can be seen that this addition method also increases the removal rate of alkali metals, but this is probably due to the increase in the interface between the AsoF3 powder and aluminum (a large amount of AsoF3 powder is added at one time). Addition of F3 can cause powder agglomeration and can reduce effective contact with aluminum). Test 7 shows the effect of the presence of the metal Mg below Li, Na and Ca. The amount of Mg after 3 minutes was 46 (removal rate: %), and after 6 minutes, it was 3 (removal rate: 70%).

It can be concluded that the presence of Mg, even at higher concentrations than other alkali metals, does not significantly adversely affect the processing efficiency. The presence of Mg in this test was due to the use of a LiF-MgF2 mixed electrolyte in the electrolytic reduction tank. The presence of magnesium in the metal from other sources (eg contamination from A-Mg alloys) may also be tolerated. However, if the M number increases,
The AsoF3 addition must be adjusted accordingly to ensure constant lithium and pinodium removal efficiency. Example 4 In two series of tests using the same equipment as in Example 3, transfer rubbo containing approximately 3400 k9 of molten aluminum each was treated according to the invention.

The AsoF3 powder was added to Rubbo in three equal parts (ie, at the start, after 3 minutes and 1 minute later) at a rate of 2.0k9 AoF3 per ton Ao. Watashisa was carried out at 178 pm for 6 minutes as in Test 3 of Example 3 to generate and maintain a stable vortex. No. 1 with American Aluminum Association symbol AA-1350 using metal treated in one test.
The metal treated in the second test was used to make a second alloy having the American Aluminum Association symbol AA-5154. The content of alkali metals and alkali metals was also determined after alloying. The results were as follows.
The average analytical value removal efficiency is comparable to that of Test 6 of Example 3.

It is also seen that the sodium and lithium concentrations continue to decrease after treatment. This is believed to be due to various metal processing operations (transfer, alloying, filtration, heating, holding, etc.) that promote the oxidation of alkali metals in the furnace. Example
5 In this example, using the same equipment and the same ASOF3 powder as in Examples 3 and 4, the molten aluminum (3500k9 each) in the transfer tube was heated at 10 pm for 10 minutes to form a stable swirl. generated and maintained.

After the treatment, the metal was allowed to stand for 1 minute and the amount of alkali metal was measured again. The results were as follows. The further reduction in alkali metal content observed after frame termination can be attributed to the high level of activity of the AsoF3-rich reaction products in contact with the molten metal. Even though such a reduction in alkali metal content during settling after processing is not significantly significant compared to the reaction during processing, it is important to note that during transfer rubbo the reduction in alkali metal content is maintained between processing and transfer to the foundry. This indicates that there is no risk of adverse reaction during the reaction. This would not occur if the alkali metal were removed by a chlorine gas reaction alone. Example
6 A series of tests were conducted to demonstrate the effect of impeller blade angle.

Using 125K9 of 997% pure molten aluminum (temperature 825K0), and using 0.8K9 of minus (1) 35M aluminum fluoride powder per 1 ton of aluminum.
It was used at a ratio of Impellers with blades of various pitches were used. d=12.5 skin, h=11 in each case
arc, d/D=0.25, h/H:0.25 and x=1
/2d. Takaazusa ran for 6 minutes at 25pm. The results were as follows. Increasing the pitch angle increases the Li removal rate after 3 and 6 minutes, and the number of vanes also appears to affect removal efficiency.

Example 7 50% (by weight) cryolite (Na3AsoF6) and 50% (by weight) cryolite (Na3AsoF6)
% (by weight) of ASOF3 (NaF/A〆F3 weight ratio = 0.43) was prepared by fusion of the above two compounds and ground to a particle size of minus (1) 35 mesh, It was used for the treatment of molten aluminum according to the invention.

Two 150k9 aluminum samples (825mm) were heated in a Lubbo medium using a 4-blade Ken-Azusa machine with a pitch angle of 30o, a diameter (d) of 12.5 arcs, a blade of 11 skins, and a height of 150k9. Processed with.

The dimensions of Rubbo are d/D ratio and h/day ratio of 0.
It was like turning 25. One of the two tests used a fluoride-containing material consisting of 85% by weight AsoF3 and 15% by weight Ame203, and the other test used a synthetic mixture of cryolite and Ame203 as described above. was used.
Both were used at a rate of 2.0 kg per ton of aluminum. The results were as follows. AsoF3/Na3
The high efficiency of the AkuF3 mixture is probably due to its low melting point (approximately 700
This is thought to be due to the formation of a phase.

Therefore, it melts after contacting the liquid aluminum and provides the A〆F3 powder for a liquid/liquid reaction rather than a solid/liquid reaction,
The ASOF3 compensates for the aluminum fluoride dilution. Furthermore, aluminum fluoride powder in a mixture with a wide range of particle size distributions was used. The average particle size at that time is from 1 willow to 0.0
I changed between 5 skins.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an apparatus for carrying out the method of the invention. FIG. 2 is a longitudinal sectional view taken along line 2--2 in FIG. Cylindrical container...
...10, Molten aluminum...11, Container cover...12, Impeller...14, Motor
Evening...16, Impeller rotating shaft...18, Blade...20, Fluoride supply port...22,
Exhaust pipe...24, vortex...26. (0.〆(o.2

Claims (1)

[Scope of Claims] 1. A method for removing contaminant alkali metals and alkaline earth metals from molten aluminum by converting such contaminant metals into fluoroaluminates by reaction with aluminum fluoride, comprising: (i) placing contaminated aluminum metal in a vertical container; (ii) constantly creating a vortex in the molten aluminum in the container and at the bottom of the vortex in the molten aluminum; (iii) stirring under conditions that produce a flow with both downward and lateral flow components and an upward swirling flow in the region near the periphery of the container; (iii) stirring the granular aluminum fluoride-containing material into the swirl; (iv) continue stirring the molten aluminum until the content of alkali metals and alkaline earth metals is reduced to a desired low level;
v) separating the molten aluminum from the molten fluoroaluminate reaction product. 2. A method according to claim 1, characterized in that the spirals are generated off-center with respect to the axis of the container. 3. The method according to claim 1 or 2, wherein a vortex is generated and maintained by a multi-impeller having blades inclined with respect to the rotation axis. 4 Powder AlF_3 or low N
4. The method according to claim 1, wherein the molten metal is treated with powdered NaF.AlF_3 in a weight ratio of aF/AlF_3. 5. The vessel has an internal diameter D and is filled to a height H with molten metal, the impeller has a diameter d and a blade height dimension h, the d/D ratio is from 0.1 to 0.6, and h/H ratio is 0
．． 4. A method according to claim 3, characterized in that it is between 1 and 0.7. 6 The axis of rotation of the impeller is 0.1 to 0.0 with respect to the axis of the container.
6. The method of claim 5, wherein the method is offset by a distance x corresponding to a value of 25D. 7 The midpoint of the blade is 0.25 to 0.7 from the bottom of the container to the top.
7. A method according to claim 6, wherein the distance y corresponds to 5H. 8 The d/D ratio is 0.15-0.40, and the impeller is 1
6. The method according to claim 5, wherein the rotation is performed at 00 to 300 rpm. 9. The method according to any one of claims 1 to 8, wherein the processing agent is supplied to the molten metal in small portions or continuously during a short period of time after the steady generation of swirls. 10 The axis of rotation of the impeller is 0.25~ with respect to the axis of the container.
6. A method according to claim 5, wherein the method is offset by a distance x corresponding to a value of 0.7d. 11. Apparatus for removing dissolved contaminants alkali metals and alkaline earth metals from molten aluminum by mixing granular aluminum fluoride-containing material with molten aluminum, the apparatus comprising: a vertical geometric axis and internal diameter D; a cylindrical container for containing molten aluminum from the bottom to a height H from the bottom surface, the cylindrical container having substantially no internal baffle; b. a multi-blade impeller for driving the impeller about a vertical axis; a cover for said container supporting means for rotating the impeller and means for dispensing the granular aluminum fluoride-containing material and discharging the fumes; The blades of the wheel have a height dimension h, the midpoint of the blades is a distance y above the bottom of the container, the axis of rotation of the impeller is a distance x from the geometric axis of the container, Their blades are at an angle θ with respect to the vertical
having a major surface slanted downwardly at; and said d
, D, h, H, x, y and θ have a d/D ratio of 0.1.
~0.6, h/H ratio 0.1-0.7, x 0.1-0
．． 25D, y is 0.25-0.75H, θ is 0-45°
The above device is characterized in that the value is such that; 12 d/D ratio is 0.15 to 0.40, h/H ratio is 0.
2-0.4, x is 0.25-0.7d, y is 0.4-0
．． 12. Device according to claim 11, characterized in that 6H and θ are 30-40°.